Crystal detector



Oct.'28, 1947 c T. H. KHIQMANY El AL 2,429,823

CRYSTAL DETECTOR Filed Aug. 2, 1946 Ifiventors I Thomas H. Kinm'an,Bertram A.C.Tuc:ker",

by M

Their AtfcOl-"fiey Patented d. 28, 1947 CRYSTAL DETECTOR Thomas H.Kinman and Bertram A. 0. Tucker, Rugby, England, assignors to GeneralElectric Company, a corporation of New York Application August 2, 1946,Serial No. 688,169 In Great Britain May 1, 1944 Section'l, Public Law690, August 8, 1946. Patent expires May 1, 1964 3 Claims.

This invention relates to the construction of pre-adjusted crystaldetectors of the silicontungsten type which have been found suitable foruse in so called microwave receivers and are particularly applicable towave-lengths within the band below 10 cms.

One object of the invention is to provide a mechanically stable assemblywhich can be handled without disturbing the catwhisker contactadjustment and which is not affected by variations in ambienttemperatures.

A further object of the invention is to fix the crystal in a positionwhere it can effectively be matched into a concentric line so that mostof the signal power is absorbed by the detector and the standing wavesset up in the line are reduced to a very small amplitude.

A crystal detector adapted for direct connection to and forming thetermination of a concentric line according to the invention comprises acylindrical metal head having an axial bore for receiving acrystal-mounting plunger adjustable therein, the crystal end of the headhaving a recess of such dimensions that, with the crystalmountingplunger in position, the crystal is mounted at a quarter wave length (oran odd multiple thereof) from the head, and a cupshaped insulatingmember secured to the head and supporting the cats whisker coaxiallywith the crystal-mounting plunger, the insulating member and catswhisker being so dimensioned as to form an effective half-wave length(or multiple thereof) connection to the central conductor of theconcentric line.

For a better understanding of the invention reference should now be madeto the drawing the single figure of which shows in cross-section theconstructional features of a crystal detector assembly embodying theinvention.

Referring to the drawing, this shows the crystal G and cat-whisker wireF which constitute a continuation of the inner conductor D of aconcentric line, and which in conjunction with outer conductor C,comprising a metal tube attached to a metal head A, terminates aconcentric line,

having substantially the same characteristic im-' pedance up to thepoint where the inner conduc- 2 be soldered firmly to an inner circularflange on the metal head A. The inner conductor is firmly attached andsupported by a soldered joint through the hole, thus effecting a rigidassembly which has been found to be proof against mechanical shock ortemperature changes after the contact adjustment. Contact adjustmentiseffected by means of a slidable plunger H to which at one end thecrystal wafer G is attached'by means of a plating and soldering process.After the contact adjustment has been made to obtain the desireddetecting characteristic, the plunger H is fixed in position by means ofa set screw J.

A flange B is provided on the head to facilitate the withdrawal of thecrystal cartridge from its holder in the end of the line.

The impedance match is effected as follows:

The length of the recess K in the metal head A and the crystal-mountingplunger constitute a wave-length sleeve which ensures that the positionof the crystal is definitely located in the line one quarter of awave-length (or an odd multiple thereof) from a point of zero potential,or short circuit. This positioning of the crystal facilitates thematching of the latter through another eifective quarter wave section,comprising the cat-whisker wire which is dimensioned and so disposed totransform the relatively high crystal impedance into the line impedancein a manner well known in concentric line practice.

The apparent mismatch introduced by the presence of the insulatingmaterial, where the latter supports the inner conductor, is offset bymaking distance from the inner to outer faces of the ceramic supportingmember on the axis an effective /2 wave-length long. This length, as iswell known, corresponds to 7\//& where )\=wave length in air ande=dielectric constant of the material. Thus, the distance between theinner and outer surface constitutes M2 and the impedance will thereforebe the same on each side of the insulation.

Crystal detectors so constructed have successfully been matched intoconcentric lines operating at wave lengths of the order of 1 cm. and themismatch introduced; expressed as a standing wave voltage ratio set upin the line and measured by means of a travelling detector has beenlessthan 1.2:1.

In the following claims Where we refer to an odd multiple or an integralmultiple of a quarter or one-half wave-length, we intend to include themultiplier one.

While we have described only a preferred embodiment of our invention byway of illustration,

1. A high frequency crystal detector arranged to be directly connectedto and to terminatea concentric transmission line comprising acylindrical metal head having anannularrecess'at;one end thereof to forma central: mountmgpost said recess having a depth equal to an oddmultiple of a quarter wave-lenth at saidirequency, a crystal.

element fixed to the end of said post, a cup-shaped insulating memberfixed to said head and enclosing said crystal element, and a centralcon-ducting member projecting through said insulating cup and carrying acats Whisker engaging said. crystal, said insulating member adjacentsaid central conducting member having a thickness effectively equal toan integral multiple of a half wavelength" at said frequency.

2. A high frequency crystal detector-"arranged tobe-directly connectedto and toterminate a concentric transmission line comprisin acylindrical metal head having an axial bore therein, a metal plungerfixed in said bore and carryin at one end a crystal element, the crystalendof said head being recessed to a depth equal to an odd multiple of aquarter wavelength at said frequency, a cup-shaped insulating memberfixed to the recessed end of said head and having centrally mounted inthe base thereof a conducting memberspacedfrom, said crystal, and acatswhisker fixed to said central conducting member and engaging saidcrystal, the base of said insulating member having a thicknesseffectively equal to an integral multiple of a half wave-length at saidfrequency.

--Athigh 'frequency crystal detector arranged be directly-cennected toand to terminate a concentric transmission line comprising a cylindricalmetal head having an axial bore therein, a metal. plunger adjustablymounted in said bore and carrying at one end a crystal wafer, thecrysta-lL-end .of said head being recessed to a depth "equal to an oddmultiple of a quarter Wave-length

